Hostname: page-component-78c5997874-lj6df Total loading time: 0 Render date: 2024-11-14T05:18:41.654Z Has data issue: false hasContentIssue false
  • English
  • Français

Aspects of simulator cone-beam CT for radiotherapy treatment planning

Published online by Cambridge University Press:  15 September 2010

Denise Irvine  and
Mark McJury
Denise Irvine*
Affiliation:
Regional Medical Physics Service, Belfast HSC Trust, Belfast, UK
Mark McJury
Affiliation:
Regional Medical Physics Service, Belfast HSC Trust, Belfast, UK
*
Correspondence to: Denise Irvine, Regional Medical Physics Service, Belfast HSC Trust, Lisburn Road, Belfast BT9 7AB, UK. E-mail: [email protected]
Get access Rights & Permissions [Opens in a new window]

Abstract

Background and purpose: Following a recent major upgrade in cone-beam computed tomography (CBCT) software and functionality, we have reassessed aspects of our Varian Acuity simulator performance for use in treatment planning. The feasibility of using CBCT for treatment planning has been assessed and here we report specifically on Hounsfield number (HN) accuracy and related dose errors, and digitally reconstructed radiograph (DRR) image quality.

Methods: Using a Catphan® 600 CT phantom, HN accuracy and uniformity were investigated for a range of CBCT imaging modes. This included the variation in HNs with scan length and phantom position. Results were compared with those acquired from conventional CT. Treatment plans for three sites were generated using the Rando phantom, and results from CBCT-based data were compared to that from CT-based data using a gamma analysis. Image quality of DRRs based on CBCT data were compared with those from CT data both quantitatively, by calculating the modulation transfer function (MTF) and qualitatively, by counting the number of line pairs visible on a phantom.

Results and conclusions: Catphan data showed that for certain cases, the HN calibration of the Acuity CBCT was out of tolerance and could lead to errors in dose calculation of >2%. HNs were only acceptable for scan lengths >10 cm. In multi-scan mode, geometric shifts and differences in HNs were seen on CT slices on either side of the interface between the two acquisitions. However, comparisons between treatment plans calculated using CBCT data and conventional CT data from Rando phantoms showed that head, pelvis and thorax plans were acceptable. CBCT DRR image quality compared favourably with a conventional CT scanner in some respects; however, image uniformity and low contrast resolution were poorer due to the ‘cupping’ artefact obtained with CBCT scans.

Keywords

cone-beam CTsimulationDRRsCT numbersHounsfield numbersimage quality
Type
Original Article
Information
Journal of Radiotherapy in Practice , Volume 9 , Issue 3 , September 2010 , pp. 165 - 174
Copyright
Copyright © Cambridge University Press 2010

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

1.Glover, GH. Compton scatter effects in CT reconstructions. Med Phys 1982; 9: 860–867.CrossRefGoogle ScholarPubMed
2.Siewerdsen, JH, Jaffray, DA. Cone-beam computed tomography with a flat-panel imager: magnitude and effects of x-ray scatter. Med Phys 2001; 28: 220–231.CrossRefGoogle ScholarPubMed
3.Jarry, G, Graham, SA, Moseley, DJ, Jaffray, DJ, Siewerdsen, JH, Verhaegen, F. Characterization of scattered radiation in kV CBCT images using Monte Carlo simulations. Med Phys 2006; 33: 4320–4329.CrossRefGoogle ScholarPubMed
4.Ding, GX, Duggan, DM, Coffey, CW. Characteristics of kilovoltage x-ray beams used for cone-beam computed tomography in radiation therapy. Phys Med Biol 2007; 52: 1595–1615.CrossRefGoogle ScholarPubMed
5.Varian Acuity ConeBeam CT Customer Release Notes, version 2.0, June 2006.Google Scholar
6.Kearns, D, McJury, M, Commissioning a new CT simulator I: CT simulator hardware. J Radiother Pract 2007; 6: 153–162.CrossRefGoogle Scholar
7.Kilby, W, Sage, J, Rabett, V. Tolerance levels for quality assurance of electron density values generated from CT in radiotherapy treatment planning. Phys Med Biol 2002; 47: 1485–1492.CrossRefGoogle ScholarPubMed
8.Knöös, T, Nilsson, M, Ahlgren, L. A method for conversion of Hounsfield number to electron density and prediction of macroscopic pair production cross-sections. Radiother Oncol 1986; 5: 337–345.CrossRefGoogle ScholarPubMed
9.Droege, RT, Morin, RL. A practical method to measure the MTF of CT scanners. Med Phys 1982; 9: 758–760.CrossRefGoogle ScholarPubMed